Heating and cooling for residential, commercial and institutional building is typically provided through combustion of natural gas, heating oil, propane or resistive electric heating. District energy systems are being adopted in high density urban locations. Such systems typically involve large upfront investments in central plants and require very large pipes to distribute the heat energy, which are very intrusive and expensive to deploy. High temperature fluid for heating (the reverse for cooling) is distributed to buildings which, in turn, typically use air handlers to distribute the heat or cool within buildings. Accordingly, the pipe diameter limits the amount of heat being distributed and its cost to implement limits the number of buildings that can be connected to the system. However, geo-exchange systems are gaining in popularity as these systems provide heating and cooling energy efficiently and use renewable heat energy from the ground.
Generally, geo-exchange systems incorporate a ground-source heat pump (GSHP) and a ground loop, also called a ground heat exchanger (GHX). Heat pumps enable energy efficient fuel switching to electricity which itself is increasingly renewable as solar and wind prices drop. In particular, while GSHPs are energy efficient, in urban areas, however, they command a very high capital cost for the ground loop. In many jurisdictions, electricity is significantly more expensive than natural gas and therefore the operating cost can also be high, and therefore reducing the operating cost of a GSHP improves the economic return of geo-exchange.
Moreover, GSHP performance varies over the course of the heating or cooling system. In the case of heating, performance is high at the start of winter but drops as heat is removed from the ground. A GSHP's effective coefficient of performance (COP) is an average over the season. If the heat energy balance is not maintained over the course of a year, the ground loop can chill (or warm) such that GSHP performance worsens over time and the economic cost increases. However, GHXs are generally regarded as expensive heat sources or heat sinks because of the cost of drilling of boreholes that accommodate conduits carrying the working fluid. The size of the GHX is determined by both the peak heating demand and the net heat demand over a season. Accordingly, reducing the size of the GHX required will improve the economic return for geo-exchange.
It is an object of the present invention to mitigate or obviate at least one of the above-mentioned disadvantages.